The lost wax investment casting process may be used to manufacture a variety of items, including jewelry, ornaments, figurines, dental components and industrial parts. In the lost wax investment casting process, a wax or plastic pattern of an item may be created by, for example, injecting wax or plastic into a rubber or metal mold, or by hand carving. These patterns 11 may then be attached to a sprue 10 to create a pattern or casting “tree” 13, such as that illustrated in FIGS. 1A and 1B. The sprue 10 is typically a constant diameter cylinder formed of solid wax or plastic by extrusion or injection molding. The sprue 10 may be mounted in a base 12 that may hold the sprue 10 in a substantially stable orientation. The base 12 may comprise a cone 14 for holding the sprue 10, and lip 16 for sealing the base 12 to a flask (not shown).
The wax or plastic patterns 11 may be affixed to the sprue 10 using a variety of methods and tools, such as with softened wax or plastic or with adhesive. The finished tree 13 may then be placed in a container called a flask (not shown). The base 12 may serve as a base or lid for the flask. Powdered investment material and water may be mixed. The investment mixture may be poured into the flask, submerging the tree 13 of patterns 11. After the investment mixture solidifies, the flask may be heated to cure the investment material to strengthen it into an investment mold into which molten metal may be poured. The base 12 may be removed after the investment mold has set and before heating. During the flask “curing” process, the patterns 11 and sprue 10 may be melted and/or burned out of the investment mold, leaving mold cavities of the pattern shape and channels into which molten metal may flow. The patterns may also be removed by chemical dissolution. Once the curing and burnout process is complete, the flask may be placed in a casting machine. Molten metal may then be poured into the investment mold. The cavity created in the investment mold by the cone 14 of the base 12 may serve to funnel the molten metal into the channels and pattern cavities formed in the investment mold by the tree. After the metal solidifies, the investment mold may be removed, and the cast objects may be cut from the tree and finished.
Using a solid wax or plastic sprue may result in increased wax or plastic material costs, in increased burnout emissions and byproducts, in trees that bend or twist as patterns are attached to the tree, in relatively large sprues that leave correspondingly large channels to be filled by molten metal, and in excessively wide channels that increase turbulence of molten metal as it flows into the flask. For example, if the sprue bends or twists in the flask, some patterns may be pushed closer to one side of the flask, resulting in an investment mold that is weaker in that area. Greater mold non-uniformity may increase the risk that the investment mold will break during curing and use. There exists a need for a method and apparatus for reducing or eliminating one or more of those disadvantages.